Portable communication devices generally use power conservation strategies having duty cycles of alternating power on and power off times to prolong the life of an energy storage device, such as a battery. Many of today's automobiles have a portable communication device such as an automobile transceiver module which receives radio frequency (RF) communications from one-way communicating key fobs for functions such as automobile door unlock. Two-way communicating key fobs which include a RF transceiver capable of both transmitting signals to and receiving signals from the automobile transceiver module can provide additional remote functionality but are preferably designed with low complexity and power conservation for small size in order to be easily hand held and low power consumption design tolerance to provide long battery life.
While a short duty cycle on the RF transceiver of the automobile transceiver module reduces the energy use below that of a continuously operating transceiver so that the automobile's battery is not drained by the transceiver module's operation, the period of power control is sufficiently short to allow for vehicle functionality in response to a key fob with very low latency. Use of a similar duty cycle and power control period for the RF transceiver of the key fob would quickly drain a small battery thereof. The key fob's RF transceiver should be capable of providing reliable communication with the automobile transceiver module without undue power consumption of the key fob's battery. In addition, sufficient range capability between the vehicle and the key fob greatly reduces concerns with system latency for the automatic communication of vehicle information to the key fob. Thus, a power conservation strategy having a relatively low duty cycle and a long period can be utilized by the key fob without significantly impacting the usefulness of the radio frequency communication system. Therefore, to accommodate the relatively low duty cycle operation of the key fob transceiver circuitry for signal reception, communications between the vehicle transceiver and the key fob transceiver circuitry should be synchronized to minimize power consumption.
Accordingly, it is desirable to provide a vehicle transceiver module with a power conservation duty cycle which quickly detects signals from key fob transceivers during power on times to minimize energy consumption and a key fob transceiver which detects signals from the vehicle transceiver with increased latency but significantly reduced power consumption. In addition, it is desirable to provide a method for synchronous communication systems which provides power conservation while providing for quick synchronization between multiple transceivers. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.